The blow-by gas is the gas that leaks out from the combustion chamber of an internal combustion engine of a motor vehicle or the like via the gap between the piston and the cylinder, and contains uncombusted hydrocarbons (HC) and carbon monoxide (CO). As such substances are a cause of pollution of the atmosphere, the PCV (positive crankcase ventilation) system is widely used. In the PCV system, the blow-by gas is returned to the intake system to burn the blow-by gas with the mixture, instead of releasing the blow-by gas to the atmosphere. However, if the amount of the blow-by gas that is returned to the intake system is increased excessively, the performance of the engine may be impaired. Therefore, a PCV valve is commonly used for adjusting the flow rate of the blow-by gas.
A PCV valve may consist of a differential pressure actuated flow rate control valve that adjusts the valve opening according to the pressure difference between the upstream and downstream ends of the valve. When the engine is stationary, as there is no pressure difference, the PCV valve fully closes. If the surrounding temperature is low, the moisture in the intake air may freeze in the PCV valve. In such a case, even when the engine is started and a pressure difference is created between the inlet and outlet ends of the PCV valve, the valve member may be kept fixed so that the PCV valve remains fully closed. Thus, when the flow passage for blow-by gas is blocked owing to the freezing of moisture in the PCV valve, the pressure in the crankcase rises, and this could cause the leakage of oil from the engine, and even seizure of bearings. Therefore, various proposals have been made to prevent the freezing of moisture in the PCV valve.
There are primarily two approaches to prevent freezing in a PCV valve. The first is to use the heat produced from the engine. The second is to use a device specifically designed for heating the PCV valve. Patent Document 1 proposes an arrangement based on the second approach that uses an electric heater for heating the valve member. The electric heater includes a bobbin having an inner surface forming a part of the inner surface of the valve case and a coil wound around the bobbin.